28 June 1999 Design of a near-field probe for optical recording using a three-dimensional finite-difference time-domain method
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The data density of the optical recording medium depends on the focused beam spot size, which is limited by diffraction. Near-field optical techniques using evanescent light have been developed to overcome the diffraction limit of the far-field optics. In particular, Betzig et al. have applied a scanning near-field optical microscope (SNOM) for magneto-optical recording. The resolution of the metal coated tapered SNOM probe is limited by the aperture size and not by the farfield diffraction limit. A resolution less than 60nm was demonstrated. However, low efficiency of the throughput of this probe limits the speed of read-out and recording. In other research, Terris et al. have developed near-field optical recording optics using the solid immersion lens (SIL). The advantage of SIL is a high optical throughput which is larger than that of conventional SNOM probe. However, there is technical difficulty in keeping the position of the relatively large flat bottom of the SIL in the near-field of the recording medium. Recently, Ghislain et al. developed a tapered SIL whose bottom is a sharp conical shape to improve the positioning of the SIL probe. We designed an alternative tapered probe whose bottom is flat, table shaped and 1/n wavelength in diameter. This diameter is large enough to propagate the incident light without significant decay of the amplitude. This probe shape also can be easily made by using a conventional lithography technique and can be applied to the flying—head for nearfield optical recording. The probe shapes and optical configurations are schematically illustrated in Fig.l. In this study, we employed three dimensional (3D) FDTD model to compute the electromagnetic field of this probe optics. A full-vector computation method of electromagnetic field, which based on the Maxwell’s equations, is necessary to design a practical near-field probe. Arbitrary probe shapes and geometries can be modeled using the 3D-FDTD method.
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Kusato Hirota, Tomas D. Milster, Yan Zhang, "Design of a near-field probe for optical recording using a three-dimensional finite-difference time-domain method", Proc. SPIE 3864, Joint International Symposium on Optical Memory and Optical Data Storage 1999, 38642B (28 June 1999); doi: 10.1117/12.997635; https://doi.org/10.1117/12.997635

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